This invention relates to an improvement to pneumatic guns, air rifles, pellet rifles, paintball guns and the like. Such pneumatic guns are typically driven by either hand or electrically cocked springs, compressed gas, or hand operated pumps and suffer from a number of disadvantages outlined in more detail below.
Air rifles have been around for many years and have seen numerous evolutionary changes over the years. The most common methods for propelling the projectile use the energy from compressed gas or from a spring. There are four major techniques shown in the prior art for launching the projectile with many variations based upon such teachings. These techniques include: (i) the use of stored compressed gas in the form of carbon dioxide cylinders or other high pressure storage tanks; (ii) using a powerful spring to push a piston which compresses air which then pushes the projectile; (iii) using a hand pump to pressurize the air for subsequent release; and (iv) using a direct acting means such as a solenoid plunger or centrifugal force to push the projectile out of the barrel. All of these methods have distinct disadvantages when compared to the present invention.
The first technique requires a source of compressed air, such as a tank or canister. Filling, transporting and using such a canister represents an inconvenience and potential safety hazard for the user. Often, additional equipment such as regulators, evaporation chambers, and other controls are required to reduce the pressure in the cylinder to a level suitable for launching the projectile. This peripheral equipment increases the cost and complexity of such an air gun. Additionally, for carbon dioxide driven air or paintball guns, the velocity of the projectile can vary significantly depending on the canister temperature. Furthermore, these tanks store a large amount of energy which, can be suddenly released through a tank fault, creating a potential safety issue. Additional teachings such as those contained in U.S. Pat. Nos. 6,516,791, 6,474,326, 5,727,538 and 6,532,949 teach of various ways of porting and controlling high pressure air supplies to improve the reliability of air guns (specifically paintball guns and the like) by differentiating between the air stream which is delivered to the bolt which facilitates chambering the projectile and the air stream which pushes the projectile out of the barrel. All of these patents still suffer from the major inconvenience and potential safety hazard of storing a large volume of highly compressed gas within the air gun. Additionally, as they combine electronic control with the propulsion method of stored compressed gas, the inherent complexity of the mechanism increases, thus, increasing cost and reliability issues. An additional teaching in this area in U.S. Pat. No. 6,142,137 shows an electrical means to assist in the trigger control of a compressed air gun. In this patent, an electromotive device is used in conjunction with electronics to define various modes of fire control such as single shot, burst or automatic modes. This addresses the ability of multiple modes of fire, but does not solve the fundamental propulsion issues of safety and inconvenience associated with gas cylinders.
A second technique which has been used for quite a few years in many different types of pellet, “bb” or air rifles has a basic principle of storing energy in a spring which is subsequently released to rapidly compress air. The highly compressed air created by a spring acting on a piston pushes the projectile out of the barrel at high velocity. Problems with this method include the need to “cock” the spring between shots thus limiting its use to single shot devices and low rates of fire. Furthermore, the unwinding of the spring results in a double recoil effect. The first recoil is from the initial forward movement of the spring, but a second recoil occurs when the spring slams the piston into the end of the cylinder (i.e. forward recoil). Additionally, spring air rifles require a significant amount of maintenance and, if dry-fired, the mechanism is easily damaged. Finally, the effort required for such “cocking” is often substantial and can be difficult for many individuals. References to these style air guns can be found in U.S. Pat. Nos. 3,128,753, 3,212,490, 3,523,538, and 1,830,763. Additional variations on the above technique have been attempted through the years including using an electric motor to cock the spring that drives a piston. This variation is detailed in U.S. Pat. Nos. 4,899,717 and 5,129,383. While this innovation solves the problem of cocking effort, the resulting air rifle still suffers from a complicated mechanism, double recoil and maintenance issues associated with the spring piston system. Another mechanism which uses a motor to wind a spring is shown in U.S. Pat. Nos. 5,261,384 and 6,564,788. Herein, a motor is used to compress a spring which is connected to a piston. The spring is subsequently quickly released allowing it to drive a piston compressing air which pushes a projectile out the barrel. This implementation still suffers from similar limitations inherent in the spring piston systems. Hu teaches of using a motor to wind a spring in these patents. Because there is no compression valve, the spring must quickly compress the air against the projectile to force it out the barrel at good velocity. This requires a strong spring to rapidly compress the air when the mechanism releases. Springs in such systems are highly stressed mechanical elements that are prone to breakage and which increase the weight of the air gun. A further disadvantage of Hu's teaching is that the spring is released from the rack pinion under full load causing the tips of the gear teeth to undergo severe tip loading. This causes high stress and wear on the mechanism especially the gear teeth. This is the major complaint for those guns in the commercial market and is a major reliability issue with this style mechanism. A further disadvantage of this type of mechanism is that upon scale up to accept larger projectiles or projectile with more energy, there occurs much increased wear and a forward recoil which is the result of the piston impacting the front end of the cylinder. In a dry fire (no projectile), the mechanism can be damaged as the piston slams against the face of the cylinder. Hu teaches use of a breech shutoff, that is common in virtually all toy guns since the air must be directed down the barrel and the flow into the projectile inlet port must be minimized. Hu specifically does not incorporate an air compression valve in his patents which is a restrictive valve against which the piston compresses the air for subsequent release. Thus, forward recoil, high wear and low power are drawbacks in these types of mechanisms. A similar reference can be seen in U.S. Pat. No. 1,447,458 which shows a spring winding and then delivery to a piston to compress air and propel a projectile. In this case, the device is for non-portable operation.
The third technique, using a hand pump to pressurize the air, is often used on low end devices and suffers from the need to pump the air gun between 2 to 10 times to build up enough air supply for sufficient projectile velocity. This again limits the air rifle or paintball gun to slow rates of fire. Additionally, because of the delay between when the air is compressed and when the compressed air is released to the projectile, variations in the projectile velocity are quite common in these style air guns. Further taught in U.S. Pat. Nos. 2,568,432 and 2,834,332 is a method to use a solenoid to directly move a piston which compresses air and forces the projectile out of the air rifle. While this solves the obvious problem of manually pumping a chamber up in order to fire a gun, these devices suffer from the inability to store sufficient energy in the air stream. Solenoids are inefficient devices and can only convert very limited amounts of energy due to their operation. Furthermore, since the air stream is coupled directly to the projectile in this technique as it is in spring piston designs, the projectile begins to move as the air is being compressed. This limits the ability of the solenoid to store energy in the air stream to a very short time period and further relegates its use to low energy air rifles. In order to improve the design, the piston must actuate in an extremely fast time frame in order to prevent significant projectile movement during the compression stroke. This results in a very energetic piston mass similar to that shown in spring piston designs and further results in the undesirable double recoil effect as the piston mass must come to a halt. Additionally, this technique suffers from dry-fire in that the air is compressed between the piston and the projectile. A missing projectile allows the air to communicate to the atmosphere through the barrel and can damage the mechanism in a dry-fire scenario. Another variant of this approach is disclosed in U.S. Pat. No. 1,375,653, which uses an internal combustion engine instead of a solenoid to act against the piston. Although this solves the issue of sufficient power, it is no longer considered an air rifle as it becomes a combustion driven gun. Moreover, it suffers from the aforementioned disadvantages including complexity and difficulty in controlling the firing sequence. Further taught in U.S. Pat. Nos. 4,137,893 and 2,398,813 to Swisher is the use of an air compressor coupled to a storage tank which is then coupled to the air gun. Although this solves the issue of double recoil, it is not suitable to a portable system due to inefficiencies of compressing air and the large tank volume required. This type of system is quite similar to existing paintball guns in that the air is supplied via a tank and not compressed on demand. Using air in this fashion is inefficient and not suitable for portable operation since much of the air compression energy is lost to the environment thru the air tank via cooling. Forty percent or more (depending on the compression ratio) of the compressed air energy is stored as heat and is lost to do work when the air is allowed to cool. Furthermore, additional complexity and expense is required to regulate the air pressure from the tank so that the projectile velocity is repeatably controlled. A variation of the above is to use a direct air compressor as shown in U.S. Pat. No. 1,743,576. Again, due to the large volume of air between the compression means and the projectile, much of the heat of compression is lost leading to inefficient operation. Additionally, this patent teaches of a continuously operating device which suffers from a significant lock time (time between trigger pull and projectile leaving the barrel) as well as the inability to run in a semiautomatic or single shot mode. Further disadvantages of this device include the pulsating characteristics of the air stream which are caused by the release and reseating of the check valve during normal operation.
The fourth technique is to use direct mechanical action on the projectile itself. The teachings in U.S. Pat. Nos. 1,343,127 and 2,550,887 represent such mechanisms. Limitations of this approach include difficulty in achieving high projectile velocity since the transfer of energy must be done extremely rapidly between the impacting hammer and the projectile. Further limitations include the need to absorb a significant impact as the solenoid plunger must stop and return for the next projectile. This causes a double-recoil or forward recoil. Since the solenoid plunger represents a significant fraction of the moving mass (i.e. it often exceeds the projectile weight), this type of system is very inefficient and limited to low velocity, low energy air guns as may be found in toys and the like. Variations of this method include those disclosed in U.S. Pat. No. 4,694,815 in which a hammer driven by a spring contacts the projectile. The spring is “cocked” via an electric motor, but again, this does not overcome the prior mentioned limitations.
All of the currently available devices suffer from one or more of the following disadvantages:                1. Manual operation by cocking a spring or pumping up an air chamber.        2. Difficult to selectively perform single fire, semiautomatic, burst or automatic modes.        3. Inconvenience, safety and consistency issues associated with refilling, transport and use of high-pressure gas or carbon dioxide cylinders.        4. Non-portability and low efficiency. Carnival air rifles and the like are tethered to a compressed air supply powered by a compressor which loses a significant portion of the energy of compression to heat loss from the air tank thus making battery operation impractical.        5. Forward recoil effects, high wear, and dry fire damage associated with spring piston and electrically actuated spring piston designs.        6. Complicated mechanisms associated with electrically winding and releasing a spring piston design resulting in expensive mechanisms with reliability issues.        7. Inefficient use and/or coupling of the compressed air to the projectile resulting in low energy projectiles and large energy input requirements.        